Open-loop power control enhancement for blind rescue channel operation

Abstract

A method and apparatus for determining an efficient and reliable power level for the MS's transmitter for reverse link communications during a rescue procedure to rescue dropped calls quickly and with a high success rate is disclosed. A mobile station's mean rescue transmission output power level is computed by first determining the mobile station's mean receive input power level when the mobile station transmits during a connection rescue procedure. This mean receive input power level is then adjusted using up to four parameters. These four variables include (1) a pre-rescue power delta, (2) a rescue interference delta, (3) a rescue delay compensation value, and (4) a pre-determined value.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]Embodiments of the present invention claim priority from U.S. provisional patent application Ser. No. 60 / 262,689 entitled “Open-Loop Power Control Enhancement for Blind Rescue Channel Operation,” filed Jan. 19, 2001, and are related to U.S. utility application Ser. No. 09 / 978,974 entitled “Forward Link Based Rescue Channel Method and Apparatus for Telecommunication Systems,” filed Oct. 16, 2001, the contents of which are incorporated herein by reference for all purposes.BACKGROUND OF THE INVENTION[0002]1. Field of the Invention[0003]The present invention relates, generally, to communication network management and, in one embodiment, to a method and apparatus for utilizing open-loop power control to control the transmit power of a mobile station transmitter during a connection rescue procedure.[0004]2. Description of Related ArtINTRODUCTION[0005]Rather than just providing a means for emergency communications, cellular telephones are rapidl...

AI Technical Summary

Benefits of technology

[0055]The pre-rescue power delta is computed by subtracting the MS's mean receive power level from the MS's transmit power level at the time of the last transmission of the power control group (power control bits) by the network before a rescue is triggered. When MS transmission is started during rescue, the MS's mean rescue transmission output power level may be computed by adding the pre-rescue power delta to the negative of the mean rescue receive input power level to compensate for the lack of closed loop power control in the rescue period.

[0057]The MS may also add a rescue delay compensation value to the MS's mean rescue transmission output power level to account for the increased uncertainty in computing a new mean rescue transmission output power level as the time t between the start of the fade and start of the MS's transmission increases. Generally, as t increases, more uncertainty is introduced in computing a new MS transmit power level and the more desirable it may be to boost the initial rescue transmission power level.

[0058]In addition to the above-described adjustments that may be made by the MS, the MS may receive from the network, prior to rescue, a pre-determined value to be added to the MS's mean rescue transmission output power level to compensate for delays, uncertainty in the missing closed loop power control, or to increase the chance of a successful rescue. This pre-determined value may be specified by the network or a standard.

Problems solved by technology

Dropped connections can range from being a nuisance to devastating for cellular telephone users.

For example, a dropped emergency 911 connection can be critical or even fatal.

Dropped connections can create consumer frustration significant enough to cause the consumer to change service providers.

However, because there are practical limitations on the number of MSs that can be simultaneously paged using one paging channel, some BSs may employ multiple paging channels.

The practical limit of signal reception depends on the channel conditions and interference level.

Types of interference include those generated when the signal is propagated through a multi-path channel, signals transmitted to and from other users in the same or other cell sites, as well as self-interference or noise generated at the device or MS.

However, noise and interference in the field may require error correction to determine what was actually transmitted.

When the data is combined through maximum ratio combining or other similar combining algorithms, the data from a strong channel may be weighted more heavily than data from a weak channel, which is likely to have more errors.

It should be noted, however, that the new active set may not always exactly comply with the MS's request, because the network may have BS resource considerations to deal with.

Soft handoff allows a MS to maintain communication with one or more BSs (sectors) simultaneously while the condition of any one of these links is not sufficient to allow successful communication through a single link.

Layer 2 Acknowledgment Failures and Forward Link Fade Failures may occur because of excessively high frame error rates or bursty error rates.

In a practical communications network, it is neither realistic nor desirable to target an error rate of zero percent (i.e., all frames received properly).

In this example, if the frame error rate rises above one percent, then the power control loop might increase the power of signals transmitted by the MS so that the frame error rate decreases to approximately one percent.

Despite the aforementioned power control loop, error rates may not be controllable to about one percent as a MS, which has limited transmitter power, moves about in a cellular network and experiences variations in signal strength and signal quality due to physical impediments, interference from adjacent channels, and positions near the edges of sectors.

As the error rates rise to intolerable levels, dropped connections become a problem.

However, closed loop power control is supplied because the uplink (reverse link) and downlink (forward link) may experience different signal environments called a forward / reverse link imbalance.

However, the last power level used by the connection is likely to be near maximum power because prior to the connection failure, the connection was likely experiencing high frame error rates and therefore was likely to have been power controlled towards maximum power levels by the network.

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